1. Field of the Invention
The present invention relates to a vibrating gyroscope and more particularly to a piezoelectric vibrating gyroscope.
2. Description of the Related Art
As a piezoelectric vibrating gyroscope, generally there is a type where the vibrator is composed of a vibrating reed and a type where the vibrator is composed of a tuning fork. Further, among vibrators to be used in piezoelectric vibrating gyroscopes, there are a type where the vibrator itself is made of a piezoelectric ceramic material and electrode films constituting a detecting element and a drive element are formed thereon and a type where the vibrator is made of a member material producing mechanical vibration such as an elastic metal and piezoelectric elements constituting a detecting element and a drive element are formed thereon.
In these vibrating gyroscopes, a bending displacement of a vibrator due to a Coriolis force generated at the time when a rotational angular velocity is applied to the vibrator is changed into an electrical signal by using a piezoelectric material and an electrical output in proportion to the rotational angular velocity is obtained through a detecting circuit.
A conventional example of a signal processing circuit to process detection signals output from a vibrator in these vibrating gyroscopes is explained with reference to FIG. 3.
In FIG. 3, reference numeral 1 represents a vibrator. The vibrator 1 is provided with a vibrating body 2, two detecting elements 3a and 3b and a driving element 3c. The two detecting element 3a and 3b are connected to the input stages of buffer amplifiers 4a and 4b through wirings 7a and 7b, respectively. Further, the wirings 7a and 7b are connected to a reference voltage Vref through load resistors RL, respectively. The output from the buffer amplifier 4a is input to an adder 5 and a differential circuit 6, and in the same way the output from the buffer amplifier 4b is input to the adder 5 and the differential circuit 6. Then, the output signal from the adder 5 is fed back to a drive circuit 11, and the output signal as an angular velocity detection signal from the differential circuit 6 is output to a next stage constituting a circuit for treatment of the detection signal.
The above-explained conventional vibrating gyroscope has the following problems.
That is, in the circuit for processing the detection signal in the conventional vibrating gyroscope, parasitic capacitances Csa and Csb are generated between the wirings 7a and 7b connected to the vibrator 1 and a ground (or a reference voltage), respectively.
Although these parasitic capacitances Csa and Csb had little adverse effect when the vibrator 1 was of a large size and the electrical signal obtained by piezoelectric effect was large, with miniaturization of the vibrator 1 in recent years the capacitance of piezoelectric elements as a detecting element was reduced and the effect of the above parasitic capacitances became not negligible, and this caused variations in level and phase of the output signals from the two detecting element 3a and 3b. 
It is possible to suppress these variations by making the parasitic capacitances Csa and Csb equal, but in order to equalize them it is required that the wirings 7a and 7b. connecting the two detecting element 3a and 3b and the buffer amplifiers 4a and 4b be formed so as to have the same length and width and to be symmetric with each other.
However, in order to form wirings meeting the above conditions, many new restrictions were put on the design of wirings and these restrictions became main causes to hinder miniaturization of the circuit board.
Further, when the circuit board where a circuit pattern meeting the above conditions is formed is put into a vibrating gyroscope unit, new parasitic capacitances (affecting the circuit) generated between the circuit pattern and other elements such as the case of the unit excluding the circuit affected the circuit.
Further, when the operating conditions (temperature, humidity, etc.) of the vibrating gyroscope unit were changed, the parasitic capacitances were altered causing variations in level and phase of the output signals from the vibrator.
Therefore, it is an object of the present invention to provide a vibrating gyroscope where the above-mentioned problems are solved, where the occurrence of problems due to the parasitic capacitance and variations of the parasitic capacitance is suppressed, and where stabilization of the output signals are made possible.
The present invention reduces the variations of characteristics of a vibrating gyroscope by applying a circuit technique of a driven shield to the circuit construction and by suppressing the generation itself of parasitic capacitance.
The vibrating gyroscope comprises: a vibrator having a plurality of detecting elements and a driving element; a plurality of amplifiers for amplifying detection signals from the respective detecting elements; a plurality of wirings respectively connected between the plurality of detecting elements and the plurality of amplifiers and shielded with an electric potential based on an output of the amplifiers.
According to the present invention, even if there is a difference in wiring between a plurality of connecting means, the parasitic capacitances at the input stages of the amplifiers become zero. Therefore, various problems due to the parasitic capacitances can be solved.
For example, in designing circuits, the patterning of the circuits and the constructional design in consideration of generation of differences in parasitic capacitances become unnecessary and accordingly the freedom of designing is increased and miniaturization of the vibrating gyroscope becomes possible.
Even if environments change, the differences in parasitic capacitances are not altered, and accordingly the change of output signals of a vibrator is caused only by the change of the proper characteristics of the vibrator. Therefore, the effect of the environments on the output signal from a vibrating gyroscope is reduced, and because the change of the output signal is due to the proper characteristics of the vibrator, the correction in other circuits becomes easy and a more stable and more reliable output signal from the vibrating gyroscope can be obtained.
In addition, the output from the adding means is made nearly the same in amplitude as each of the plurality of output means, and accordingly it becomes possible to protect the connecting means from parasitic capacitances by a driven shield using the output signal of the adding means. This makes using an output from each of the amplifiers unnecessary. Because of this, when the circuit is made an IC, the number of pins can be reduced and further, because the circuit pattern of each of the driven shields is at the same potential, the freedom in designing the circuit patterns is increased, the vibrating gyroscope is more reduced in size and the cost of designing the vibrating gyroscope is decreased.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.